Myosin mRNA accumulation and myofibrillogenesis at the myotendinous junction of stretched muscle fibers.
Myosin mRNA accumulation and myofibrillogenesis at the myotendinous junction of stretched muscle fibers.
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DOI：
10.1083/jcb.111.5.1885
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发表时间：
1990-11
期刊：
影响因子：
--
通讯作者：
Eisenberg BR
中科院分区：
文献类型：
--
作者：
Dix DJ;Eisenberg BR
用原位杂交、免疫荧光和电子显微镜研究了牵张肥大兔骨骼肌肌腱连接处的肌纤维生长和肌原纤维组装。原位杂交发现延长4d的纤维在MTJ处有较高水平的肌球蛋白重链(MHC)mRNA。在这些延长的纤维的MTJ处的电子显微镜下，发现一个大的细胞质空间，没有肌原纤维，但含有多聚体、肌浆网和T膜、线粒体、高尔基复合体和新生细丝组件。来自电子显微镜的结果表明，肌原纤维在拉伸纤维中的组装遵循一系列事件。(A)在伸展的纤维末端，几乎整个肌膜都是电子致密的，但只有一部分附着着肌原纤维。免疫荧光检测到伸展肌肉MTJ膜上的纽蛋白显著增加。(B)在电子致密部位，细丝锚定在肌膜上。(C)以未经登记的方式与这些细丝相关的粗丝。(D)Z-小体拼接成细丝，随后细丝和粗丝落入肌小节。因此，MTJ是建立区域蛋白质合成和肌原纤维组装的mRNA积累的场所。伸展的肌肉也通过在末端增加肌管来延长。拉伸6d后，这些肌管构成了肌肉末端的大部分纤维。本质上，所有这些肌管重复初级肌管的发育程序，并表达缓慢的MHC。肌管中MHC基因的分布和肌原纤维的分布是杂乱的。
Myofiber growth and myofibril assembly at the myotendinous junction (MTJ) of stretch-hypertrophied rabbit skeletal muscle was studied by in situ hybridization, immunofluorescence, and electron microscopy. In situ hybridization identified higher levels of myosin heavy chain (MHC) mRNA at the MTJ of fibers stretched for 4 d. Electron microscopy at the MTJ of these lengthening fibers revealed a large cytoplasmic space devoid of myofibrils, but containing polysomes, sarcoplasmic reticulum and T-membranes, mitochondria, Golgi complexes, and nascent filament assemblies. Tallies from electron micrographs indicate that myofibril assembly in stretched fibers followed a set sequence of events. (a) In stretched fiber ends almost the entire sarcolemmal membrane was electron dense but only a portion had attached myofibrils. Vinculin, detected by immunofluorescence, was greatly increased at the MTJ membrane of stretched muscles. (b) Thin filaments were anchored to the sarcolemma at the electron dense sites. (c) Thick filaments associated with these thin filaments in an unregistered manner. (d) Z-bodies splice into thin filaments and subsequently thin and thick filaments fall into sarcomeric register. Thus, the MTJ is a site of mRNA accumulation which sets up regional protein synthesis and myofibril assembly. Stretched muscles also lengthen by the addition of myotubes at their ends. After 6 d of stretch these myotubes make up the majority of fibers at the muscle ends. Essentially all these myotubes repeat the developmental program of primary myotubes and express slow MHC. MHC mRNA distribution in myotubes is disorganized as is the distribution of their myofibrils.